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Composite Operational Excellence Score (0-100) — average percentile rank across 7 dimensions in three sub-scores: Reliability (capacity factor, forced outage days, B2B avg streak), Efficiency (fuel utilization, refuel duration), and Discipline (startup duration, scram count). 5-year window. Higher = more operationally excellent. Click to see the full breakdown.
34
Excellence
#73 of 94 ↑8
Bottom Quartile
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Days of continuous operation since the last outage ended. Clean run (no forced outages since last refueling).
182
Current Run
days ✔
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Longest recorded period of continuous operation between outages (2010-04-26 to 2011-10-17).
539
Record Run
days
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Breaker-to-Breaker runs — continuous operation exceeding the cycle-adjusted threshold (452 days for this 18-month cycle unit) with no trips to 0% power.
6
B2B Runs
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Lifetime capacity factor: average power level across all recorded days (100% = always at full power).
88.4%
Capacity Factor
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Total number of scheduled refueling outages detected in the historical data.
18
Outages
since 1999
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Average time from first power generation (>0%) to sustained full power (≥95% for 2+ days) across the last 3 scheduled outages. Click to compare against the fleet on the Operator Efficiency Leaderboard.
16.3
Avg Startup
days (last 3)
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Average fuel utilization — percent of the designed fuel cycle that this unit consumes before refueling, derived from the historical burn-down trajectory. Higher = more efficient operator (refuels with less margin remaining; closer to coastdown). Computed as 100% minus the unit's average refuel-point fuel %, using the last 3 years where available, otherwise lifetime average. Click to compare against the fleet on the Operator Efficiency Leaderboard.
96.8%
Fuel Utilization
3yr avg
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NukeWorker's Operational Excellence Score is a composite 0–100 ranking of every active US nuclear unit across 7 publicly observable performance metrics, grouped into three sub-scores:
• Reliability — capacity factor, forced outage days, B2B avg streak
• Efficiency — fuel utilization, refuel duration
• Discipline — startup duration, scram count
Each unit's metric is converted to a percentile across the active fleet. Sub-score = average of its components; composite = average of the three sub-scores. Use the time-window toggle below to switch between 3yr / 5yr / lifetime.
• Reliability — capacity factor, forced outage days, B2B avg streak
• Efficiency — fuel utilization, refuel duration
• Discipline — startup duration, scram count
Each unit's metric is converted to a percentile across the active fleet. Sub-score = average of its components; composite = average of the three sub-scores. Use the time-window toggle below to switch between 3yr / 5yr / lifetime.
Time window
— change how far back we look
NukeWorker's
Operational
Excellence Score
Operational
Excellence Score
34/100
Bottom Quartile · #73/94
5-year window
Arkansas Nuclear 1 ranks #73 of 94 active US units on NukeWorker's Operational Excellence Score over the 5-year window. Strongest area: Startup Duration (60th percentile). Weakest: Fuel Utilization (9th percentile).
Reliability
30
Capacity factor + Forced outages + B2B streaks
Efficiency
28
Fuel utilization + Refuel duration
Discipline
45
Startup duration + Scram count
Cohort Rankings
apples-to-apples comparison within each peer group
Reactor type:
#51 of 61
PWR
Containment:
#41 of 48
Dry Ambient (PWR)
Cycle length:
#43 of 54
18-month cycle
Fleet rank above (73 of 94) compares all active US units; cohort ranks compare only against units sharing this property.
Per-dimension breakdown (7 metrics)
Capacity Factor
43th
90.2% (higher better, Reliability)
Forced Outage Days/yr
14th
10.6d (lower better, Reliability)
B2B Avg Streak
33th
506d (higher better, Reliability)
Fuel Utilization
9th
94.0% (higher better, Efficiency)
Refuel Duration
47th
33d (lower better, Efficiency)
Startup Duration
60th
4.0d (lower better, Discipline)
Scrams (5-year)
30th
0.6/yr (lower better, Discipline)
Each dimension's percentile is computed across the active US fleet (94 units with sufficient history). Sub-score = average of its component percentiles. Composite = average of the three sub-scores. 5-year window. View full leaderboard →
Methodology
NukeWorker's Operational Excellence Score is a composite ranking that combines 7 publicly observable performance metrics into a single 0-100 number per US nuclear unit.
How it's computed: Each unit's raw value is converted to a percentile (0-100) within the 94 active US units that have at least 2 completed refueling cycles. The 7 percentiles are averaged into 3 sub-scores (Reliability, Efficiency, Discipline), and those are averaged into the final composite.
Active window — 5-year:
- Reliability — Capacity factor (5yr), forced outage days/yr (5yr), B2B avg streak (lifetime)
- Efficiency — in-cycle fuel utilization (3yr), median refuel duration (5yr)
- Discipline — robust mean startup duration, scrams/yr (5yr, annualised)
Cohort rankings: alongside the fleet rank, each unit gets ranked within its reactor type (PWR/BWR), containment design (Ice Condenser, Mark I, etc.), and cycle length (12/18/24-month). Useful for apples-to-apples comparisons.
What's excluded: subjective community ratings, confidential INPO ratings, financial metrics. We only use publicly available NRC + cycle data.
Why three windows? 5yr (default) is the industry standard. 3yr captures recent operational changes and post-pandemic recovery. Lifetime gives newer units a fair comparison and reveals long-term consistency.
Edge cases: units with fewer than 2 cycles (e.g., Vogtle 4) show "Provisional". Decommissioned units excluded.
Refresh cadence: recomputed daily. Each window cached separately.
A data-derived proxy for operational performance; not affiliated with INPO. INPO ratings are confidential and qualitative — ours is public and quantitative.
5-yr trend:
↑ +6.7 pts vs 2025
Compare Arkansas Nuclear 1 head-to-head with up to 3 other units.
Compare now
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Duration of each outage in days, shown chronologically. Green bars are scheduled refueling outages, red bars are forced/unscheduled. The orange dashed line marks the average duration. Extended outages (>180 days) and D&D periods are excluded.
Outage Duration Trend
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Days between consecutive scheduled refueling outage starts, showing operating cycle regularity. The purple dashed line marks the average cycle length. Most U.S. reactors operate on 18-month (547 day) or 24-month (730 day) cycles.
Cycle Length History
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Time in days from first power generation (>0%) to sustained full power (≥95% for 2+ consecutive days) after each scheduled refueling outage. The dashed line marks the average. Includes startup testing holds and power dips.
Startup Duration Trend
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Estimated fuel remaining in the current cycle, expressed as a percentage of the unit's typical cycle. Starts at 100% when the unit returns to power post-refuel and drops as full-power-days are burned. Days at reduced power burn fuel proportionally — so a unit with significant downtime (high burn deficit) drops slower and ends up with MORE fuel left than its calendar position would suggest. Coastdown threshold around 15%. Toggle to overlay past cycles on a normalized "days into cycle" axis to see how aggressively this unit historically burns down before refuel.
Fuel Burn Down Cycle since Nov 14, 2025
64.8% remaining
180 / 507 days
1.3 FPD margin
Avg refuel: 4.0%
Avg refuel (3yr): 3.2%
Deepest burn: 0.0% (2001-04 → 2002-10)
Most margin: 14.3% (2016-12 → 2018-03)
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Monthly capacity factor with outage events overlaid as red bands. Green bars show average power level per month. Toggle to Daily view for raw daily data.
Power History
| Type ⇅ | Actual Start ⇅ | Actual End ⇅ | Duration ⇅ | Days Online ⇅ | Scheduled | Delta |
|---|---|---|---|---|---|---|
|
Scheduled
|
2025-10-11 | 2025-11-13 | 34 | 13d | 2025-10-08 | +3d |
|
Scram
# 57949
|
2025-09-25 | 2025-09-28 | 4 | 290d | - | - |
|
Unscheduled
|
2024-12-05 | 2024-12-09 | 5 | 200d | - | - |
|
Scheduled
|
2024-04-27 | 2024-05-19 | 23 | 144d | 2024-04-26 | +1d |
|
Unscheduled
|
2023-12-04 | 2023-12-05 | 2 | 291d | - | - |
|
Scram
# 56351
|
2023-02-15 | 2023-02-16 | 2 | 48d | - | - |
|
Unscheduled
|
2022-11-25 | 2022-12-29 | 35 | 2d | - | - |
|
Scheduled
|
2022-10-08 | 2022-11-23 | 47 | 311d | 2022-10-08 | 0d |
|
Scram
# 55614
|
2021-11-30 | 2021-12-01 | 2 | 206d | - | - |
|
Scheduled
|
2021-04-10 | 2021-05-08 | 29 | 24d | 2021-04-10 | 0d |
|
Scram
# 55138
|
2021-03-15 | 2021-03-17 | 3 | 483d | - | - |
|
Scheduled
|
2019-10-06 | 2019-11-18 | 44 | 289d | 2019-09-16 | +20d |
|
Scram
# 53793
|
2018-12-19 | 2018-12-21 | 3 | 176d | - | - |
|
Unscheduled
|
2018-06-23 | 2018-06-26 | 4 | 5d | - | - |
|
Scram
# 53459
|
2018-06-17 | 2018-06-18 | 2 | 2d | - | - |
|
Scram
# 53459
|
2018-06-13 | 2018-06-15 | 3 | 24d | - | - |
|
Scram
# 53404
|
2018-05-17 | 2018-05-20 | 4 | 2d | - | - |
|
Scheduled
|
2018-03-24 | 2018-05-15 | 53 | 311d | 2018-03-24 | 0d |
|
Scram
# 52710
|
2017-04-27 | 2017-05-17 | 21 | 136d | - | - |
|
Scheduled
SGR/Major
|
2016-09-24 | 2016-12-12 | 80 | 282d | 2016-09-18 | +6d |
|
Scram
# 51607
|
2015-12-16 | 2015-12-17 | 2 | 290d | - | - |
|
Scheduled
|
2015-01-26 | 2015-03-01 | 35 | 528d | 2015-01-25 | +1d |
|
Unscheduled
|
2013-08-15 | 2013-08-16 | 2 | 10d | - | - |
|
Scheduled
SGR/Major
|
2013-03-25 | 2013-08-05 | 134 | 491d | 2013-03-24 | +1d |
|
Scheduled
|
2011-10-17 | 2011-11-20 | 35 | 539d | 2011-10-16 | +1d |
|
Unscheduled
|
2010-04-19 | 2010-04-26 | 8 | 2d | - | - |
|
Scheduled
|
2010-03-22 | 2010-04-17 | 27 | 406d | 2010-04-20 | -29d |
|
Unscheduled
|
2009-02-08 | 2009-02-09 | 2 | 2d | - | - |
|
Unscheduled
|
2009-02-06 | 2009-02-06 | 1 | 45d | - | - |
|
Unscheduled
|
2008-12-21 | 2008-12-23 | 3 | 10d | - | - |
|
Scheduled
|
2008-10-27 | 2008-12-11 | 46 | 533d | 2008-10-26 | +1d |
|
Scheduled
|
2007-04-23 | 2007-05-13 | 21 | 480d | 2007-04-22 | +1d |
|
Unscheduled
|
2005-12-27 | 2005-12-29 | 3 | 6d | - | - |
|
Scheduled
SGR/Major
|
2005-10-05 | 2005-12-21 | 78 | 473d | 2005-10-04 | +1d |
|
Unscheduled
|
2004-06-12 | 2004-06-19 | 8 | 31d | - | - |
|
Scheduled
|
2004-04-21 | 2004-05-12 | 22 | 133d | 2004-04-20 | +1d |
|
Unscheduled
|
2003-11-16 | 2003-12-10 | 25 | 78d | - | - |
|
Unscheduled
|
2003-08-30 | 2003-08-30 | 1 | 291d | - | - |
|
Scheduled
|
2002-10-05 | 2002-11-12 | 39 | 437d | 2002-10-05 | 0d |
|
Unscheduled
|
2001-07-25 | 2001-07-25 | 1 | 108d | - | - |
|
Scheduled
|
2001-03-17 | 2001-04-08 | 23 | 70d | 2001-03-17 | 0d |
|
Unscheduled
|
2001-01-06 | 2001-01-06 | 1 | 298d | - | - |
|
Unscheduled
|
2000-03-14 | 2000-03-14 | 1 | 2d | - | - |
|
Unscheduled
|
2000-02-05 | 2000-03-12 | 37 | 25d | - | - |
|
Unscheduled
|
2000-01-08 | 2000-01-11 | 4 | 91d | - | - |
|
Scheduled
|
1999-09-11 | 1999-10-09 | 29 | 249d | 1999-09-11 | 0d |
|
Unscheduled
|
1999-01-01 | 1999-01-05 | 5 | - | - | - |
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